Clinical applications of characteristic frequency measurements: preliminary in vivo study.

In vivo electrical impedance tomography images have been available for some years, and most of them show variation in impedance amplitude between two different states, for example between inspiration and expiration of the lungs. A refinement of the tomography technique has made it possible to show images of the complex impedance of the body. If several frequencies are used, more information on the investigated tissues can be collected, and new areas made available for investigation. It has been shown that tissues exhibit a characteristic frequency that can be derived from the maximum magnitude of the (negative) reactance. The characteristic frequency-related images can be calculated from several imaginary part curves obtained using the back-projection technique. The paper shows in vivo impedance spectra from different parts of the body, determines the characteristic frequency of the different in vivo measurements and suggests different applications of characteristic frequency imaging. Several data sets are collected to show the reproducibility of the measurements.